The present invention generally relates to aircraft electric power systems, and more particularly to a power system for a high efficiency auxiliary power unit (APU) system.
Many current aircraft electric power systems are 3-phase AC at 400 Hz and the electrical generators are required to produce power at a constant frequency of 400 Hz. The synchronous generators installed on auxiliary power units, named APU generators herein, also produce 400 Hz without the need for a constant speed drive mechanism, because the APUs have a constant speed.
Since an APU is sized for worst-case operating conditions of ground altitude and ground temperature, it may be operated more efficiently at lower speeds for much of the time, which saves fuel. Since the APU generator output frequency is proportional to its speed a method to obtain 400 Hz power from the APU generator when running the APU at lower speeds may be needed.
Airport infrastructures may not provide conditioned air to an aircraft when at an airport gate. Many aircraft use the APU to produce pressurized air to run an Environmental Control System (ECS) of the aircraft. This method of providing conditioned air burns fuel which increases overall operating cost as well as emissions. A method for operating the aircraft ECS using electrical power from the airport gate is very desirable.
An Electric Green Taxi System may provide fuel savings by taxiing the airplane using electric motors, powered via power controllers from the APU generator. The additional weight associated with such systems may reduce the fuel savings so weight mitigation is desirable.
In view of the foregoing, there is a need for high efficiency low weight aircraft power systems to reduce fuel consumption and emissions.